Mechanical seals are commonplace in many industries for providing a seal between rotating and stationary components. The seal is created by one sealing face rotating against another stationary sealing face. Commonly, one of these faces is urged toward the other through the use of springs thus providing the required sealing force. The amount of spring force is optimised so that the operational life of the seal is as long as possible whilst the volume of fluid that passes between the faces is kept to a minimum. The more fluid that passes between the faces means that the operational life will be longer whilst this also means that emissions into the atmosphere and loss or contamination of potentially costly product fluid is increased. If virtually no fluid passes between the faces then the operational life will be shorter due to more of the face material being in contact thereby generating more heat and reducing the length of time before the seal faces are degraded to a point where the leaked volume of fluid is no longer controlled. This is known as a seal failure.
The amount of spring force is controlled in seal designs by maintaining a consistent level of compression through maintaining the physical clearances between components during assembly and operation of the seal. This is commonly done through the use of setting clips which set the distance that the rotary components are spaced from the stationary components; however due to space or design constraints this is not always possible.
The majority of reactors and agitators in the world are dependent upon the performance of a canisterised mechanical seal, which in turn is entirely dependent upon the tolerances, particularly the axial tolerances of the equipment inside which it is encased. An example of where this is not easily possible is mixer seals that are used on Lightnin Agitator applications. In these applications the gland encases the seal making it impossible to access the internal workings of the seal and easily access any traditional setting means that ensure correct alignment and installation of the seal on the equipment. The installer is therefore reliant on the tolerances and/or final assembly of the equipment being correct to provide the correct spring forces for the mechanical seal to operate as desired.